1. Field of the Invention
This invention relates to a method for treating wastewaters with an adsorbent and a rotating biological contactor.
2. Description of the Prior Art
A variety of methods are available for the biological treatment of sewage and industrial wastewaters. Commonly used methods are the activated sludge process using air and pure oxygen and the trickling filter. More recently the rotating biological contactor, e.g. as described in Welch U.S. Pat. No. 3,557,954, Jan. 26, 1971, has found application in which a series of discs on a common shaft is rotated in the body of the wastewater alternately immersing a biological film formed on the disc in the liquid and exposing the film to the air above the liquid to provide oxygen for maintaining a biological film on the surface of the disc to effect biological oxidation of the wastewater. Reduced energy consumption for oxygen transfer is claimed in such a system which can be designed for a variety of applications ranging from ordinary carbonaceous BOD.sub.5 removal to biological nitrification.
The broad concept of passing wastewater in countercurrent flow with continuously moving activated carbon to remove organic content of the water is disclosed by Timpe et al. U.S. Pat. No. 3,763,040, Oct. 2, 1973.
More recently, it has been suggested that powdered activated carbon be added to the activated sludge process to effect improvements in performance of the activated sludge system as taught in Hutton et al. U.S. Pat. No. 3,904,518, Sept. 9, 1975. Benefits claimed are improved stability, improved liquid solids separation, and a higher degree of treatment. The method taught in U.S. Pat. No. 3,904,518 is a single stage suspended slurry contact system in which the carbon is contacted only with the equilibrium concentration of adsorbable organics in the wastewater in the presence of activated sludge. For more efficient contact of the carbon with adsorbable material, it is desirable to effect a countercurrent contact with water to expose the carbon incrementally or continuously to a higher concentration of adsorbable material in the wastewater.